The invention concerns a method for the closed-loop speed control of an internal combustion engine.
The speed of a drive unit is typically automatically controlled to an idling speed and a final speed. A drive unit is understood to mean either an internal combustion engine-transmission unit or an internal combustion engine-generator unit. To achieve closed-loop speed control, the speed of the crankshaft is detected as a controlled value and compared with an engine speed set value, i.e., the reference input. The resulting control deviation is converted by a speed controller to a correcting variable for the internal combustion engine, for example, an injection quantity. The problem with a control loop of this type is that torsional oscillations, which are superimposed on the controlled value, can be amplified by the speed controller. This can lead to instability of the closed-loop control system
The problem of instability is countered by a speed filter in the feedback path of the closed-loop speed control system. EP 0 059 585 B1 describes a speed filter of this type, in which the timing values of a shaft teeth are detected by means of an operating cycle of the internal combustion engine. The operating cycle is defined as two revolutions of the crankshaft, corresponding to 720°. These tooth timing values are then used to calculate a filtered tooth timing value by taking the arithmetic mean. This filtered tooth timing value corresponds to the filtered actual speed value, which is then used for the automatic control of the internal combustion engine.
A closed-loop speed control system for automatically controlling a drive unit with a speed filter of this type in the feedback path is described, for example, in DE 199 53 767 C2.
However, the problem with this two-revolution filter in the feedback path is that stable behavior of the drive unit is accompanied by deterioration of the design load behavior.